Loongson: Replace the system clock provided by the CPU with a GLX MFGPT.

CPU throttling was not possible due to the fact that the system clock
was the CPU clock. So slowing down the CPU would also slow down the
passing of time.

This commit adds a driver for the MFGPT1 clock from the AMD companion
chip found on lemote and hooks it up as the system clock.

It also changes the frequency value of hz from the default, which was
100, to 128. That's because the scaling on MFGPT clocks is represented
by powers of two.

Okay miod@.

Move glxpcib(4) to MI land unifying the two MD drivers.

Specific features of the companion chip will be handled in MD land.

Okay deraadt@.